Screening is currently the most effective way for early detection of colonic cancer. Computed tomographic colonography (CTC), or virtual colonoscopy, has become an effective technique for non-invasive colon cancer screening that can be an alternative to optical colonoscopy (OC). However, current CTC examinations require pre-examination cathartic bowel preparation, essentially identical to that required for OC. The perceived discomfort and inconvenience associated with the rigorous cathartic bowel preparation before a CTC examination has been identified as the main barrier to wide acceptance of colon screening. The main technical barrier in applying non-cathartic bowel preparation to CTC examination is the lack of an effective electronic cleansing (EC) scheme for subtraction of tagged fecal materials in CTC images, because the cleansing artifacts encountered in current EC methods are too severe to allow non-cathartic CTC images of diagnostic quality. Dual-energy CT (deCT) is a new imaging technique that allows materials differentiation based on CT attenuation values derived from two synchronous CT acquisitions at different energies. Non-cathartic dual-energy CTC (deCTC), i.e., applying deCT to non-cathartic CTC image acquisition, has the potential significantly to improve the quality of EC. In this project, we will develop an EC scheme for non-cathartic deCTC, denoted as dual-energy EC (deEC), in which patients will be examined with non-cathartic bowel preparation and imaged with a deCT scanner. After image acquisition, the proposed deEC scheme will effectively remove the residual fecal materials in the colon in CTC images by a set of novel image processing methods developed in a dual-energy context. The capability of material differentiation in deCTC provides a new dimension for obviating the major cleansing artifacts existing in current EC methods, and thus provides CTC images of diagnostic quality. For evaluation purposes, we will establish a non-cathartic DE-CTC database. The quality and performance of the proposed DE-EC scheme will be evaluated in a phantom study, a manual cleansing study, a computer-aided detection (CAD) of polyps study, and an observer study. This research is innovative in that the non-cathartic deCTC and the development of its deEC scheme have not yet been attempted. The successful development and validation of the proposed deEC scheme will provide radiologists with cleansed CTC images of diagnostic quality for detecting colon cancer, and it will release the patients from the main concern regarding colon screening. Such an deEC-aided non-cathartic deCTC examination could substantially increase the screening compliance, safety, and the capacity for colon cancer screening. Thus, the proposed research will substantially raise the screening rate and the early detection of colonic polyps and cancers.